Semiconductors are used in integrated circuits for electronic applications, including radios, televisions, cell phones, and personal computing devices, as examples. One type of semiconductor device is a semiconductor storage device, such as a dynamic random access memory (DRAM) or flash memory, which use electric charge to store information.
A recent development in semiconductor memory devices involves spin electronics, which combines semiconductor technology and magnetics. The spin of electrons, rather than the charge, is used to indicate the presence of binary states “1” and “0.” One such spin electronic device is a magnetic random access memory (MRAM) device, which includes conductive lines (wordlines and bitlines) and a magnetic stack or magnetic tunnel junction (MTJ), which functions as a magnetic memory cell. A sufficient current flowing through the conductive lines can generate enough magnetic field to orient the polarity of the magnetic films in the magnetic memory cell into a certain direction. Digital information, represented as a “0” or “1,” is storable in the alignment of magnetic moments in the magnetic memory cell films. The resistance of the magnetic memory cell depends on the magnetic moment alignment, and is used as an indicator the binary state of the device.
MRAM devices are typically arranged in an array of rows and columns, and the wordlines and bitlines are activated to access each individual memory cell. In a cross-point cell (XPC) MRAM array, current is run through the particular wordlines and bitlines to select a particular magnetic memory cell. In a field effect transistor (FET) array cell, each MTJ is disposed proximate to a FET, and the FET for each MTJ is used to select a particular magnetic memory cell in the array. In a FET array, an electrode is typically formed between the MTJ and the FET to make electrical contact between the MTJ and the FET.
An advantage of MRAM devices compared to traditional semiconductor memory devices such as (DRAM) devices is that MRAM devices are non-volatile. For example, a personal computer (PC) utilizing MRAM devices would not have a long “boot-up” time as with conventional PCs that utilize DRAM devices. Also, an MRAM device does not need to be continually powered to “remember” the stored data. Therefore, it is expected that MRAM devices will replace flash memory, DRAM and static random access memory devices (SRAM) devices in electronic applications where a low-power, high performance memory device is needed.
Because MRAM devices operate differently than traditional memory devices and because they are relatively new, they introduce design and manufacturing challenges.